1. Field of the Invention
The present invention relates to an image data verification system for detecting an alteration in image data generated by an image generation device such as a digital camera.
2. Related Background Art
In recent years, digital cameras for storing an optical image of a subject by digitizing the optical image have commercially practical.
Although image data obtained by a digital camera can be easily imported to a personal computer, it also can be easily altered in the personal computer. Consequently, there is a problem that image data obtained by a digital camera is inferior to that of a film photo in reliability, and therefore, in admissibility of evidence. In view of such a circumstance, a digital camera system with a function of adding a digital signature to the image data obtained by the digital camera has been proposed in recent years. Conventional digital camera systems with a digital signature function are disclosed in U.S. Pat. No. 5,499,294, Japanese Patent Application Laid-Open No. 9-200730 and so on.
In order to generate a digital signature, the public key cryptography as the RSA encryption is typically used. However, the public key cryptography system such as the RSA encryption, which requires exponentiation and remainder calculation, can hardly realize a high speed processing, and requires a processing time hundreds or thousands times longer than that of the common key cryptography such as the DES. Therefore, there is a problem that it is quite difficult with the restricted calculation resource of the conventional digital camera to generate a digital signature. While there may be contemplated a method for allowing the digital signature to be generated easily by enhancing significantly the performance of the calculation resource of the conventional digital camera, this method is not preferred because the cost of the digital camera itself is significantly increased.